Process for reducing pilling in textile articles



United States Patent 3,396,446 PROCESS FOR REDUCING PILLING 1N TEXTILE ARTICLES Philip W. Eggleston, William Glen, Kenneth W. Hillier,

and Ian Marshall, Harrogate, England, assignors to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain No Drawing. Continuation-impart of application Ser. No. 147,669, Oct. 19, 1961. This application Sept. 24, 1965, Ser. No. 490,123 Claims priority, application Great Britain, May 31, 1955,

15,545/55 8 Claims. (Cl. 28-76) This is a continuation-in-part of US. application Ser. No. 147,669, filed Oct. 19, 1961, now abandoned, which in turn is a continuation-in-part of U.S. application Ser. No. 586,367, filed May 22, 1956, now abandoned.

This invention relates to the manufacture of improved textile articles made from fibres of synthetic linear polymers, such as the polyamides and the highly polymeric polymethylene terephthalates.

The fibres of synthetic linear polymers, such as the polyamides and the highly polymeric polymethylene terephthalates are made by cutting or breaking continuous filaments, usually when they are in the form of a tow. These fibres are then formed into spun yarns by any known method.

Textile articles made from these spun yarns show a tendency to form fluff, small balls or pills of loose fibres when these articles are subjected to abrasion on themselves or with other surfaces, as happens in normal wear. This formation of fluff, small balls or pills is difficult to remove from the surface of the fabrics. For the sake of brevity the phenomenon is hereinafter called pilling.

According to our invention we provide a process for reducing the tendency to pilling in articles made from spun yarn consisting of synthetic linear polymers, such as the highly polymeric polymethylene terephthalates, characterized in that the polymer in the form of filaments or fibres is treated to reduce the molecular weight of the polymer, for example, as measured by intrinsic viscosity, to within the range 0.28 to 0.45. It will be appreciated that other methods of assessing the molecular weight can be used, such as the determination of the relative viscosity, or simply the flow-time or the polymer in solution in a suitable solvent, such as in orthochlorophenol in the case of polyethylene terephthalate and similar polyesters derived from terephthalic acid.

The molecular weight can be reduced in any stage of manufacture; that is to say it can be reduced by treating the filaments before these are converted into fibres or the fibres as such, or when spun into yarn can be treated, when woven or knitted into fabrics, or the articles made up from the fabrics may be treated.

Many methods may be used for reducing the molecular weight of the polymer in the filaments or fibres, but care must be taken that the reduction in molecular weight is not carried too far, so that the fibres do not lose their useful textile properties. Tenacity and abrasion resistance, for example, are reduced with the reduction of the molecular weight, as well as the tendency to pilling. A balance must therefore be found for each type of polymer when the molecular weight is reduced, so that the tendency to pilling is reduced sufficiently, but other textile properties such as the tenacity and abrasion resistance are still sutficient for the particular textile application for which the fibres are to be used. For polyethylene terephthalate, the reduced molecular weight in terms of intrinsic viscosity is 0.28- 0.45.

It will be appreciated that when the treatment of our 3,396,446 Patented Aug. 13, 1968 ice invention is applied to polyethylene terephthalate, the intrinsic viscosity should be reduced to between 0.28 and 0.45, because at these values the tendency to pilling is eliminated or at least reduced considerably. If the intrinsic viscosity is to be reduced to these values, one may use any polymer having an initial intrinsic viscosity above those figures. Clearly, the shorter and/ or less intense treatment will be required, if the initial viscosity of the polymer is only just above the stated values, namely above 0.45. However, it is generally the practice to begin with a polyethylene terephthalate having a minimum intrinsic viscosity of 0.56. Polyethylene terephthalates having a minimum viscosity of about 0.63 have been found useful.

The treatment for reducing the molecular weight is preferably carried out at elevated temperatures in order to limit the time of treatment to a minimum. For the same reason superatmospheric pressure may be used.

When treating the filaments or fibres in order to reduce the molecular weight, care should be taken that no appreciable dissolving of the polymer from which the fibres have been made up, takes place.

The highly polymeric polymethylene terephthalates, such as polyethylene terephthalate can be treated to reduce the molecular weight of the filaments or fibres using known polymer degradation techniques, such as superheated steam. Another method comprises an amidation treatment using aqueous solutions of ammonia, ammonia vapour or amines. Other suitable methods comprise treatments with concentrated nitric acid or sulphide solutions, such as sodium sulphide. A variety of such procedures are described in the literature, and no limitation to the specific agents list is intended.

It will be appreciated that in order to obtain uniform results and to avoid e.g. uneven dyeing, that the treatment should be applied uniformly. This may be achieved by reducing gradients of temperature and moisture in the treating zone to a minimum. In some treatments the reduction of the molecular weight of the polymer may be accompanied by a chemical change, e.g. the treatment of polyethylene terephthalate with ammonia, which is thought to result in amidation.

In the process of our invention a polymer having the molecular weight usually associated with commercial fibre formation is treated while in filament or fibre form to reduce the molecular weight. This reduction of molecular weight is an essential part of our invention.

We believe that by the treatment of our invention the rate of formation of the pills is balanced by the rate of removal because the pills when formed rub off or fall off.

The method of measuring the molecular weight may be carried out by determining the intrinsic viscosity, which is then converted to values of average molecular Weight.

The intrinsic viscosity is determined as follows:

A sample of the fibres is accurately weighed and dissolved in a solvent, the solution is introduced into an Ostwald Viscometer nd the flow time is determined. The ratio:

f low time of solution fiow time of solvent is the specific viscosity from which the intrinsic viscosity (I.V.) is calculated according to the formula,

Where (SV) is the specific viscosity and (C) is the concentration of the solution in grams per ml.

In the case of polyethylene terephthalate 0.25 gram of the fibres are weighed accurately and dissolved in 25 ml. of orthochlorophenol having a boiling point of 176 C., by heating at 100 C. for l5-30 minutes, after 3 cooling the flow time in a No. 2 B.S.S Ostwald Viscometer is determined at a temperature of 25 C. to +0.1" C. The concentration of the solution (C) is expressed in grams dissolved in 100 ml. at 25 C.

As stated above, when the treatment of our invention is applied to polyethylene terephthalate it is necessary to reduce the intrinsic viscosity from about 0.63 to between 0.28 to 0.45. At these values the tendency to pilling is eliminated or at least reduced considerably. The molecular weight can also be determined as the relative viscosity, which is the ratio of the viscosity of a solution of the polymer in a solvent to the viscosity of the solvent alone. For example, as measured at 25 C. in a 10 percent weight/volume solution in a mixture of 10 parts of phenol and 7 parts of 2,4,6-trichlorophenol (by weight), a polyethylene terephthalate which has an intrinsic viscosity of 0.28 to 0.45 has a relative viscosity of about 8 to 16.

Since it is an object of our invention to reduce the pilling of the fabrics made from spun yarns consisting of synthetic linear polymers, it is convenient to use a comparative pilling test. We have measured the pilling of our samples by tumbling 4 samples at a time, 4 /2" x 5 /2" in size of the fabrics, wrapped round rubber tubes about 1" in diameter and 6 /2" long. The samples are tumbled in a cubiod shaped box of about 9" side length, lined with cork, for a period of 5 hours at 60 r.p.m. The samples are inspected at intervals and any occurrence of pilling noted.

The following examples illustrate, but do not limit our invention.

Example 1 Polyethylene terephthalate fabric samples were prepared by knitting from a 2/36s (wool count) polyethylene terephthalate yarn, using 3 denier 4-inch staple fibres. The samples were degraded by amidation with ammonia solution having a specific gravity of 0.88 for 18, 42 and 66 hours, respectively in a sealed aspirator, at room temperature. During this treatment, the yarn tenacity was reduced gradually from 2.6 grams per denier in the untreated sample to 0.82 g.p.d.; the extension at break was reduced from 27.7% to 10.5%; the intrinsic viscosity was reduced during this treatment from 0.59 to 0.38, which corresponds approximately to a reduction in the number average molecular weight from 10,500 in the untreated sample to 5,600 after treatment for 66 hours. The abrasion resistance, which was measured by abrading the samples to destruction, ranged from 100,000 revolutions of the abrasion tester of the untreated sample to 7,000 revolutions on the sample treated for 66 hours. Pilling of the sample was measured and the number of pills per square inch counted. On the untreated sample, there were 47.5 pills per square inch, compared with no pills on the sample treated for 66 hours. The results are given in the attached table. Optimum results were obtained by the treatment for 42 hours, the number of pills per square inch being only 2. In this sample the individual fibre tenacity was reduced to 2.2 from the original fibre tenacity in the untreated sample of 3.7 grams per denier.

4 N The yarn tenacity during the treatment was reduced from 2.3 g.p.d. in the untreated sample to 1.64 and 0.89 g.p.d. after treatment for 18 to 42 hours, respectively.

Extension at break was reduced from 27.0% on the untreated sample to 26.3v and 16.4, after treating for 18 and 42 hours, respectively, whereas the intrinsic viscosity was reduced from 0.56 on the untreated sample to 0.45 and.0.35 respectively, which corresponds to a'number average molecular weight of 9,750 on the untreated sample and 7,250 and 5,000 after treatment for 18 and 42 hours. The corresponding relative viscosities as measured at 25 C. in a 10% weight/volume solution in a mixture of 10' parts of phenol and 7 parts 2,4,6-trichlorophenol (by weight) are 16 and 11. The abrasion resistance was reduced from 22,000 revolutions of the abrasion tester to 14,500 and 6,000 revolutions after the treat ment for 18 and 42 hours, respectively. The number of pills per square inch was 12.5 in the untreated sample and no pilling occurred on a comparative test after the samples had been treated for 18 to 42 hours.

Example 3 Polyethylene terephthalate fabric samples prepared by weaving as in Example 2 were treated with steam in a pressure cooker at 40 lb. per square inch for 6 hours. Dnr- Example 4 A pleated skirt obtained by weaving 1/18s (cotton count) yarn using 3 denier 1 /2 inch polyethylene terephthalate fibres, was treated in aqueous ammonia solution of a specific gravity of 0.88 in an autoclave for 24 hours at room temperature when the molecular weight was reduced from 0.62 to 0.45. A pilling test carried out on the treated sample showed that the tendency to pilling was reduced from 12 to 1 pill per square inch. The pleats in the skirt remained unchanged.

From these results, in the examples, it can be seen that it is necessary to reduce the intrinsic viscosity of polyethylene terephthalate fibres to 0.4 or 0.45 to produce a substantial reduction in the tendency to pilling. An intrinsic viscosity of 0.4 to 0.45 corresponds to a number average molecular weight of approximately 6,000 to 7,25 0 of polyethylene terephthalate. Fabrics containing these fibres retain their excellent pleat retention and crease resistance properties but show 2 pills or less per square inch as determined by our pilling test.

Example 5 In this example filaments of polyethylene terephthalate in the form of a crimped tow were treated. The tow was loosely coiled in a regular pattern into a can and the TABLE 0.88 Ammonia Yarn Extension Intrinsic No. Average Abrasion to Pills per Treatment (hours) Tenacity at break Viscosity Molecular Destruction square inch (g. p.d.) (percent) Weight (Revolutions) (number) Example 2 treatment took place while the can was in a pressure ves- Polyethylene terephthalate fabric samples were prepared by weaving a fabric from li s (cotton count) polyethylene terephthalate yarn, using 3 denier, 1 /2" fibres. The fabric samples were degraded by amidation with an ammonia solution having a specific gravity of 0.88 as in Example 1, the time of treatment being 18 and 42 hours.

sel, with gaseous ammonia at C. and 30 lb. per square inch pressure for 45 minutes. As a result of this treatment the intrinsic viscosity of the polyethylene terephthalate was reduced from 0.62 to 0.38. The treated filament tow was cut into staple fibres. Woven fabrics were prepared 'by weaving a twill weave from 2/20s wool count yarn, using 3 denier 2% inch long polyethylene terephthalate staple fibres cut from the treated filament tow. Knitted fabrics were prepared by knitting on a gauge machine, that is to say 10 needles per inch, from a 2/ 28s worsted count yarn, using 3 denier 4 /2 long polyethylene terephthalate crimped staple fibres cut from the above treated filament tow. When these fabrics were sub- .jected to a pilling test as described, no pilling occurred. Similar fabrics made from staple fibres cut from untreated tow showed considerable pilling when tested comparatively.

Example 6 Polyethylene terephthalate filaments in the form of a tow were treated with a mixture of steam and ammonia at 130 C. and lb. per square inch pressure for minutes. The intrinsic viscosity of the polyethylene terephthalate was reduced from 0.62 to 0.48. No pilling occurred on fabrics made from staple fibre yarns, as in Example 5, when subjected to the pilling test as described. Fibres made of staple fibres cut from the untreated tow pilled badly, when tested comparatively.

Example 7 Polyethylene terephthalate filaments in the form of a tow were treated at 120 C. with gaseous ammonia at 30 lb. per square inch pressure, for 70 minutes, after preheating with steam at ,50 lb. per square inch pressure. This treatment reduced the intrinsic viscosity of the polyethylene terephthalate from 0.62 to 0.38. No pilling occurred on the fabrics made up as described in Example 5 firom staple fibres cut from the treated tow, but fabrics made from fibres cut from untreated tow, pilled badly.

Example 8 Polyethylene terephthalate crimped staple fibres were treated with 70% nitric acid at room temperature in a sealed aspirator for 24 hours. This caused a reduction in the intrinsic viscosity from 0.61 to 0.40. The treated fibres, when spun into yarn and converted into fabrics as described in Example 5, did not show any tendency to pilling, using the described pilling test. Fabrics made in the same way from untreated fibres pilled badly, when tested comparatively.

Example 9 Polyethylene terephthalate fibres in woven and knitted fabric samples were made up as described in Example 5. The fabric samples were treated for 2 hours in a 40% weight by volume solution of monomethyl amine at room temperature. The intrinsic viscosity of the polyethylene terephthalate polymer was thereby reduced from 0.62 to 0.35. No pilling was observed when the fabrics were tested but untreated fabric samples pilled badly when tested comparatively, showing 15 to 46 pills per square inch.

Example 10 A knitted fabric made from worsted spun nylon yarn was treated by immersion in a 10% solution of hydrochloric acid at 60 C. for 19 hours. The fabric, when tested for pilling as described showed no pilling after 5 hours tumbling. An untreated sample of the knitted nylon fabric, as well as samples of the fabric treated with 10% hydrochloric acid, for only 18 hours, 17 hours and 16 hours, showed considerable pilling when tested as described.

From the foregoing examples it will be seen that the improved fabrics made from spun yarn comprising the polyethylene terephthalate fibres or nylon fibres have no pills and not more than two pills per square inch when tested by tumbling in a cork lined box for 5 hours. In the case of the fabrics comprising the polyethylene terephthalate fibres, this improvement is already obtained when the intrinsic viscosity of the fibres is between 0.40 and 0.45.

The treatment of our invention gives no serious loss in the useful textile properties of the treated articles except that individual fibre strength, abrasion and wear resistance are somewhat reduced. Grease resistance and pleat retention of the articles, however, are not affected.

What is claimed is:

1. A process for improving spun yarns of polyethylene terephthalate to reduce the tendency to pilling which comprises treating a material selected from the group consisting of filaments and fibers of polyethylene terephthalate having an intrinsic viscosity of 0.56 to 0.63 to reduce the molecular weight thereof to an intrinsic viscosity between about 0.28 and 0.45 without substantially dissolving said polyethylene terephthalate.

2. A process as set forth in claim 1 in which the treatment to reduce molecular weight is effected by contacting the fibers and filaments with a member of the group consisting of steam at superatmospheric pressure, ammonia solution, gaseous ammonia, amines, concentrated nitric acid and concentrated sulfide solutions.

3. In a process for forming a polyethylene terephthalate textile fabric from fibers and filaments of polyethylene terephthalate which comprises cutting any filaments to form fibers, spinning the fibers into a spun yarn, and forming a fabric from the spun yarn; the improvement which comprises reducing the tendency to pilling of the fabric by treating filaments, fibers and fabrics of polyethylene terephthalate having an intrinsic viscosity between 0.560.63 until the intrinsic viscosity is reduced to 0.45 to 0.28 with an agent selected from the group consisting of saturated steam of about 40 pounds per square inch pressure, aqueous ammonia solution having a specific gravity of about 0.88 and at room temperature and pressure, gaseous ammonia at superatmospheric pressure of about 30 pounds per square inch and a temperature of about C., an aqueous solution of a lower alkyl primary monoamine at room temperature and cOntaining about 40% by volume of amine, and concentrated nitric acid of about 70% strength at room temperature, the steam treatment lasting for about 6 hours, the aqueous ammonia treatment lasting for at least 24 hours, the gaseous ammonia treatment lasting for about 45 minutes, the primary monoamine treatment lasting for about 2 hours and the nitric acid treatment lasting for about 24 hours, whereby the tendency of said fabric to form pills is substantially eliminated.

4. In a process for forming a polyethylene terephthalate textile fabric from fibers and filaments of polyethylene terephthalate which comprises cutting any filaments to form fibers, spinning the fibers into a spun yarn, and forming a fabric from the spun yarn; the improvement which comprises reducing the tendency to pilling of the fabric by treating filaments and fibers of polyethylene terephthalate having an intrinsic viscosity of about 0.63 until the intrinsic viscosity is reduced to 0.45 to 0.28 with saturated steam of about 40 pounds per square inch pressure for about 6 hours whereby the tendency of said fabric to form pills is substantially eliminated.

5. In a process for forming a polyethylene terephthalate textile fabric from fibers and filaments of polyethylene terephthalate which comprises cutting any filaments to form fibers, spinning the fibers into a spun yarn, and forming a fabric from the spun yarn; the improvement which comprises reducing the tendency to pilling of the fabric by treating filaments and fibers of polyethylene terephthalate having an intrinsic viscosity of about 0.63 until the intrinsic viscosity is reduced to 0.45 to 0.28 with an aqueous solution of ammonia having a specific gravity of about 0.88 and at room temperature and pressure for at least 24 hours whereby the tendency of said fabric to form pills is substantially eliminated.

6. In a process for forming a polyethylene terephthalate textile fabric from fibers and filaments of polyethylene terephthalate which comprises cutting any filaments to form fibers, spinning the fibers into a spun yarn, and forming a fabric from the spun yarn; the improvement which comprises reducing the tendency to pilling of the fabric by treating filaments and fibers of polyethylene terephthalate having an intrinsic viscosity of about 0.63 until the intrinsic viscosity is reduced to 0.45 to 0.28 With gaseous ammonia at superatmospheric pressure of about 30 pounds per square inch and at a temperature of about 130 C. for about 45 minutes whereby the tendency of said fabric to form pills is substantially eliminated.

7. In a process for forming a polyethylene terephthalate textile fabric from fibers and filaments of polyethylene terephthalate which comprises cutting any filaments to form fibers, spinning the fibers into a spun yarn, and forming a fabric from the spun yarn; the improvement which comprises reducing the tendency to pilling of the fabric by treating filaments and fibers of polyethylene terephthalate having an intrinsic viscosity of about 0.63 until the intrinsic viscosity is reduced to 0.45 to 0.28 with an aqueous solution of a lower alkyl primary monoamine at room temperature said solution containing about 40% by volume of amine, for about 2 hours whereby the tendency of said fabric to form pills is substantially eliminated.

8. In a process for formin a polyethylene terephthalate textile fabric from fibers and filaments of polyethylene terephthalate which comprises cutting any filaments to form fibers, spinning the fibers into a spun yarn, and

References Cited UNITED STATES PATETNS 2,503,251 4/1950 Edwards et al. 260 2,556,295 6/1951 Pace.

2,597,557 5/1952 Amberski.

2,865,080 12/1958 Hentschel 2872 3,104,450 9/1963 Christens et a1. 57-140 2,734,794 2/ 1956 Calton 264-282 OTHER REFERENCES Du Pont Customer Service, Dacron, Bulletins Miscellaneous, Preparation of Pill Resistant Worsted Suiting Fabrics. Section 7, pp. 3.01, 3.02.

MERVIN STEIN, Primary Examiner.

Patent No. 3,396,446

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION August 13, 1968 Philip W. Eggleston et al.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, line 17, "0.48" should read 0.38

Signed and sealed this 13th day of January 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents WILLIAM E. SCHUYLER, JR. 

1. A PROCESS FOR IMLPROVING SPUN YARNS OF POLYETHYLENE TEREPHTHALATE TO REDUCE THE TENDENCY TO PILLING WHICH COMPRISES TREATING A MATERIAL SELECTED FROM THE GROUP CONSISTING OF FILAMENTS AND FIBERS OF POLYETHYLENE TEREPHTHALATE HAVING AN INTRINSIC VISCOSITY OF 0.56 TO 0.63 TO REDUCE THE MOLECULAR WEIGHT THEREOF TO AN INTRISIC VISCOSITY BETWEEN ABOUT 0.28 AND 0.45 WITHOUT SUBSTANTIALLY DISSOLVING SAID POLYETHYLENE TEREPHTHALATE. 